“不能将float Nan转换为int”但没有Nan？

Question

我有一个数据框，并尝试进行以下操作：

data['SD_rates']=np.array([int((data['actual value'][i]-data['means'][i])/data['std'][i]) for i in range (len(data['means']))])  

它以以下消息中断：“无法将float Nan转换为int”

我理解这是一个错误，但使用data.isnull（）测试了df，并且所涉及的列均不包含NaN（我通过发送data.to_csv进行了手动控制）。

我什至用fillna（-1，inplace = True）填充了data ['std']，但它仍然中断了。 我不明白为什么，因为没有被0除（我还控制了此列中没有零，所以没有原始的0和Null / Nan用-1填充），而实际值和均值为fillna（0 ）的缺失值，无论如何减法都不能产生nan（[0-10]中的数据范围）。

有什么事吗 （如我所说，触发操作之前的数据是正确的...）。 谢谢

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这是一个代码片段：
我的假设之一是，groupby可能会生成NaN，在计算均值时我不会摆脱（但我相信熊猫会自动忽略它……）并且未填充0或-1（我故意为标准偏差选择-1以避免除以0）。

def stats_setting(data):

    print('Stats settings')
    print(data.columns)
    print(data.dtypes) 
    #sys.exit()

    data['marks']=np.log1p(data['marks'].astype(float))
    data['students']=np.log1p(data['students'].astype(float))#Rossman9 think this has to be tested
    #were filled with fillna before)

#First Part: by studentType and Assortment
    types_DoM_select=['Type','Type2','Category']

#First Block:types_DoM students grouped by categories
#wonder if can do a groupby of groupb
    print("types_DoM_marks_means")
    types_DoM_marks_means = data.groupby(types_DoM_select)['marks'].mean()
    types_DoM_marks_means.name = 'types_DoM_marks_means'
    types_DoM_marks_means = types_DoM_marks_means.reset_index()
    data = pd.merge(data, types_DoM_marks_means, on = types_DoM_select, how='left')

    print("types_DoM_students_means")
    types_DoM_students_means = data.groupby(types_DoM_select)['students'].mean() #.students won't work. Why?
    types_DoM_students_means.name = 'types_DoM_students_means'
    types_DoM_students_means=types_DoM_students_means.reset_index()    
    data = pd.merge(data, types_DoM_students_means, on = types_DoM_select, how='left')

    print("types_DoM_marks_medians")
    types_DoM_marks_medians = data.groupby(types_DoM_select)['marks'].median()
    types_DoM_marks_medians.name = 'types_DoM_marks_medians'
    types_DoM_marks_medians = types_DoM_marks_medians.reset_index()
    data = pd.merge(data, types_DoM_marks_medians, on = types_DoM_select, how='left')

    print("types_DoM_students_medians")
    types_DoM_students_medians = data.groupby(types_DoM_select)['students'].median() #.students won't work. Why?
    types_DoM_students_medians.name = 'types_DoM_students_medians'
    types_DoM_students_medians=types_DoM_students_medians.reset_index()    
    data = pd.merge(data, types_DoM_students_medians, on = types_DoM_select, how='left')
    print("types_DoM_marks_std")
    types_DoM_marks_std = data.groupby(types_DoM_select)['marks'].std()
    types_DoM_marks_std.name = 'types_DoM_marks_std'
    types_DoM_marks_std = types_DoM_marks_std.reset_index()
    data = pd.merge(data, types_DoM_marks_std, on = types_DoM_select, how='left')


    print("types_DoM_students_std")
    types_DoM_students_std = data.groupby(types_DoM_select)['students'].std()
    types_DoM_students_std.name = 'types_DoM_students_std'
    types_DoM_students_std = types_DoM_students_std.reset_index()
    data = pd.merge(data, types_DoM_students_std, on = types_DoM_select, how='left')

    data['types_DoM_marks_means'].fillna(-1, inplace=True)
    data['types_DoM_students_means'].fillna(-1, inplace=True)
    data['types_DoM_marks_medians'].fillna(-1, inplace=True)
    data['types_DoM_students_medians'].fillna(-1, inplace=True)
    data['types_DoM_marks_std'].fillna(-1, inplace=True)
    data['types_DoM_students_std'].fillna(-1, inplace=True)

#Second Part: by specific student
    student_DoM_select=['Type','Type2','Category']

#First Block:student_DoM
#wonder if can do a groupby of groupb
    print("student_DoM_marks_means")
    student_DoM_marks_means = data.groupby(student_DoM_select)['marks'].mean()
    student_DoM_marks_means.name = 'student_DoM_marks_means'
    student_DoM_marks_means = student_DoM_marks_means.reset_index()
    data = pd.merge(data, student_DoM_marks_means, on = student_DoM_select, how='left')

    print("student_DoM_students_means")
    student_DoM_students_means = data.groupby(student_DoM_select)['students'].mean() #.students won't work. Why?
    student_DoM_students_means.name = 'student_DoM_students_means'
    student_DoM_students_means=student_DoM_students_means.reset_index()    
    data = pd.merge(data, student_DoM_students_means, on = student_DoM_select, how='left')

    print("student_DoM_marks_medians")
    student_DoM_marks_medians = data.groupby(student_DoM_select)['marks'].median()
    student_DoM_marks_medians.name = 'student_DoM_marks_medians'
    student_DoM_marks_medians = student_DoM_marks_medians.reset_index()
    data = pd.merge(data, student_DoM_marks_medians, on = student_DoM_select, how='left')

    print("student_DoM_students_medians")
    student_DoM_students_medians = data.groupby(student_DoM_select)['students'].median() #.students won't work. Why?
    student_DoM_students_medians.name = 'student_DoM_students_medians'
    student_DoM_students_medians=student_DoM_students_medians.reset_index()    
    data = pd.merge(data, student_DoM_students_medians, on = student_DoM_select, how='left')

    # May I use data['marks','students','marksMean','studentsMean','marksMedian','studentsMedian']=data['marks','students','marksMean','studentsMean','marksMedian','studentsMedian'].astype(int) to spare memory?

    print("student_DoM_marks_std")
    student_DoM_marks_std = data.groupby(student_DoM_select)['marks'].std()
    student_DoM_marks_std.name = 'student_DoM_marks_std'
    student_DoM_marks_std = student_DoM_marks_std.reset_index()
    data = pd.merge(data, student_DoM_marks_std, on = student_DoM_select, how='left')

    print("student_DoM_students_std")
    student_DoM_students_std = data.groupby(student_DoM_select)['students'].std()
    student_DoM_students_std.name = 'student_DoM_students_std'
    student_DoM_students_std = student_DoM_students_std.reset_index()
    data = pd.merge(data, student_DoM_students_std, on = student_DoM_select, how='left')

    data['student_DoM_marks_means'].fillna(0, inplace=True)
    data['student_DoM_students_means'].fillna(0, inplace=True)
    data['student_DoM_marks_medians'].fillna(0, inplace=True)
    data['student_DoM_students_medians'].fillna(0, inplace=True)
    data['student_DoM_marks_std'].fillna(0, inplace=True)
    data['student_DoM_students_std'].fillna(0, inplace=True)

#Third Part: Exceptional students 

    #I think int is better here as it helps defining categories but can't use it.#    
    #print(data.isnull().sum())
    #print(data['types_DoM_marks_std'][data['types_DoM_marks_std']==0].sum())
    #data.to_csv('ex')
    #print(data.columns)

#Original version:#int raises the "can't convert Nan float to int. While there were no Nan as I verified in the data just before sending it to the    
    data['Except_student_IP2_DoM_marks_means']=np.array([int((data['student_IP2_DoM_marks_means'][i]-data['types_IP2_DoM_marks_means'][i])/data['types_IP2_DoM_students_std'][i]) for i in range (len(data['year']))])  
    data['Except_student_IP2_DoM_marks_medians']=np.array([int((data['student_IP2_DoM_marks_medians'][i]-data['types_IP2_DoM_marks_means'][i])/data['types_IP2_DoM_students_std'][i]) for i in range (len(data['year']))])  
#Second version: raises no error but final data (returned) is filled with these stupid NaN
    data['Except_student_P2M_DoM_marks_means']=np.array([np.round((data['student_DoM_marks_means'][i]-data['types_DoM_marks_means'][i])/data['types_DoM_marks_std'][i],0) for i in range (len(data['year']))])  
    data['Except_student_P2M_DoM_marks_medians']=np.array([np.round((data['student_DoM_marks_medians'][i]-data['types_DoM_marks_medians'][i])/data['types_DoM_marks_std'][i],0) for i in range (len(data['year']))])  

#End
    return data

Answer 1

您很可能是正确的，即数据框中没有Nan，但是您正在计算中创建它们。 请参阅以下内容：

In [15]: import pandas as pd
In [16]: df = pd.DataFrame([[1, 2], [0, 0]], columns=['actual value', 'col2'])
         df['means'] = df.mean(axis=1)
         df['std'] = df.std(axis=1)

In [17]: df
Out[17]:
   actual value  col2  means  std
0             1     2    1.5  0.5
1             0     0    0.0  0.0

因此，数据框没有任何Nans，但是计算呢？

In [21]: [(df['actual value'][i]-df['means'][i])/df['std'][i] for i in range (len(df['means']))]
Out[21]: [-1.0, nan]

现在，当您对int进行调用时，您会在结果列表中得到一个错误。 最后，我建议（如果可能的话）直接在基础数组中执行操作，而不要使用for循环，因为这样会更快。

In [25]: (df['actual value']-df['means'])/df['std']
Out[25]:
0    -1
1   NaN
dtype: float64

但是，这可能是不可能的，具体取决于所需的0除法返回值。